Involvement of spindles in memory consolidation is slow wave sleep-specific

“…this association was more pronounced during deep sleep than during light sleep, the pertaining correlation coefficients were contrasted directly (Meng et al. 1992), revealing a significantly stronger link between memory retention and spindle density during SWS than during stage 2 sleep (Z ¼…”

“Sleep architecture parameters were not associated with memory retention either, which is in line with some studies (e.g., Clemens et al. 2006), but not others (e.g., Takashima et al. 2006).”

“As such, the temporal coupling of hippocampal ripples, sleep spindles, and slow oscillations might reflect a hippocampo-cortical di- alogue underlying system-level memory consolidation during sleep (Buzsáki 1996; Born et al. 2006).”

“They are generated by the interplay of cells of the thalamic reticular nucleus and thalamocortical relay neurons (Steriade 2006), although their duration is also affected by neocortical feedback (Bonjean et al. 2011).”

“Our observed spindle densities are roughly similar to values obtained with other detection algorithms in both EEG (Gais et al. 2002; Mölle et al. 2011) and intracortical (Peter-Derex et al. 2012) studies, suggesting that our finding is not an artifact stemming from the spindle algorithm used.”

“Importantly, slow oscillations have a naturally occurring grouping influence on spindles (Mölle et al. 2002; Clemens et al. 2007), and such focusing of spindle rhythms into the active slow oscillation up-state increases after a learning episode (Mölle et al. 2009).”

“It should be mentioned that we do not claim that sleep spindles during light sleep are completely unrelated to memory processing, as various studies have demonstrated otherwise (e.g., Gais et al. 2002; Schabus et al. 2008; Tamaki et al. 2008).”

“As such, the temporal coupling of hippocampal ripples, sleep spindles, and slow oscillations might reflect a hippocampo-cortical di- alogue underlying system-level memory consolidation during sleep (Buzsáki 1996; Born et al. 2006).”

“Furthermore, indicators of sleep spindle expression consistently correlated with the amount of overnight retention of declarative memories (86, 213, 214, 235, 446, 562, 822, 1016, 1024, 1037, 1044, 1057).”

“As spindle power averaged across SWS of the entire stimulation period did not differ between conditions (Figure S1), these observations indicate that in-phase stimulation chiefly enhanced the synchronization of spindles to the SO and corroborates findings showing that the synchrony with the SO cycle rather than the am…”

“Altogether, the emerging picture challenges the view that phase coupling of NREMsleep rhythms and associatedmemory formation is under the sole or primary control of the cortical slow oscillation (Cox et al., 2012; Diekelmann and Born, 2010; Steriade, 2006), instead revealing a critical contribution of thalamic spindle…”